Gas analyzer and a method for operating the same

ABSTRACT

A gas analyzer having an analysis or sensor unit and having an electronic processing unit, and a method for operating such a gas analyzer. In order to achieve substantially improved safety both in handling corrosive and/or combustible and/or toxic gases in a not potentially explosive atmosphere (ex-free atmosphere), and in the operation of such an analyzer in an ex-atmosphere, the analysis or sensor unit as such is of non-explosive configuration and is arranged in a gas tight chamber through which a toxic and/or corrosive and/or combustible gas flows and around which a second chamber is arranged.

1. FIELD OF THE INVENTION

This invention relates to a gas analyzer having an analysis or sensorunit and having an electronic processing unit, and to a method foroperating such a gas analyzer.

2. Description of the Prior Art

Many versions, and also many operating methods, are known for gasanalyzers having a sensing unit and an electronic processing unit. Inthis case, use is made of gas sensors which, depending on configuration,are sensitively set to one or other gases depending on which one isdesired for selective measurement. Electronic sensor systems, gelsensors, thermal conduction sensors and other similar sensors are knownfor this purpose. Solid electrolyte sensors are also known, inparticular for oxygen analysis.

Also known, however, over and above this are optical gas analysismethods in the case of which a cuvette flowed through by measuring gasis transradiated starting from a light source of specific radiationbands. Arranged on the side of the cuvette opposite the light source isa detector which picks up a measurement signal based on an optopneumaticeffect. The detector is sensitively set to the measuring gas componentto be measured, and measures the residual signal remaining in terms ofabsorption after passage through the cuvette. This is inverselyproportional to the partial pressure fraction of the measuring gascomponent in the measured gas sample. Because of this inverselyproportional relationship, so-called absorption spectroscopy is alsoinvolved here. Such methods are generally used as absorption photometerswith appropriate light sources.

In the case of use in process measurement techniques, that is to say inonline measurement of industrial process cycles, for the most part gassamples are taken which are sent via the analyzer. Explosion protectionprecautions are to be taken for the eventuality that the gases are toxicor combustible.

In chemical process engineering, however, it is frequently necessary tosolve measurement tasks in which one or more gas components in corrosiveand/or toxic and/or combustible gases are to be analyzed. As a rule, theextractive measurement techniques currently on offer have specialproperties in order to meet the requirements of measurement techniquesand safety. For this purpose, expensive use is made of specialists whoare employed in potentially explosive atmospheres (ex-atmospheres) andalso in corrosive and toxic gases together with housing purging(pressurized enclosure) and a pressure tight enclosure, that are to bemonitored. It frequently happens that some damage has already occurredbefore the service staff can intervene.

It is therefore the object of the invention to improve a gas analyzerand a method for operating such in order substantially to improve safetyboth in handling corrosive and/or combustible and/or toxic gases in anot potentially explosive atmosphere (ex-free atmosphere) and in theoperation of such an analyzer in an ex-atmosphere.

SUMMARY OF THE INVENTION

The solution according to the invention takes account in this case bothfor the gas analyzer and for the operating method both in the first casein which combustible gases are to be analysed in the ex-free atmosphere,and of the second case, in which the combustible gas is present in anex-atmosphere. In the second-named case, it is necessary to addappropriate configurations, as described below.

Likewise to be distinguished are the gas analyzer groups alreadydescribed at the beginning in the prior art. These are, firstly, thegroup of optical gas analyzers and also others such as the group ofthermal conduction sensors and solid electrolyte or gel sensors.

The second-named case corresponds in essence to a gas analyzer inaccordance with claim 1. The core of the invention there consists inthat in the case of the analysis of a toxic and/or corrosive and/orcombustible gas the analysis or sensor unit as such is of non-explosive(for example intrinsically safe) configuration and is arranged in agastight chamber around which a second chamber is arranged. This case isthat of a gas analyzer with an integrated sensor unit and integratedprocessing unit.

However, these are arranged in a common housing in separate parts of thesame. The sensor region arranged inside the housing is correspondinglyprovided with a non-combustible sensor which is arranged in a firstchamber, the second chamber then being arranged around this firstchamber and thus being placed between a first chamber, containing thesensor, and the remaining space, in which the electronic system isarranged. This yields an appropriately ex-protected separation betweenthe sensor chamber and electronic system. If toxic or combustible orcorrosive gases are then fed to the sensor, they remain basically insidethe first chamber, which contains the sensor. For safety purposes, thesecond chamber, which is arranged around the first chamber, shields thelatter in turn.

It is provided in an appropriate refinement in the case of this variantapparatus that the second chamber is purged with an inert gas or withair. If a leak were to occur in this case through the first chamber,toxic or corrosive or combustible measuring gas would flow via thisleakage only into the second chamber, which is, in turn, purgedpermanently by an inert gas. The effect, in turn, is to dispose of theleakage gas into a closed purging gas system, the leakage gas therebybeing simultaneously substantially thinned by the purging. Consequently,in the way provided by the invention, not only is leakage counteracted,but leakage and/or the dangerous gas emerging because of the leakage canbe diluted until it is unobjectionable, and thereby be branded safe.

In a second independent device claim, the correspondingly identicalmethodology is applied to an analyzer which is based on an opticaldetection method such as, for example, on absorption photometry. In thiscase, the element of corresponding consideration is the cuvette. Thecuvette contains a measuring gas inlet and a measuring gas outlet. Thatis to say there is no gas contact with the detector as such, and thecuvette remains a closed system. In order now to fulfil theex-protection preconditions in the way according to the invention, thesaid cuvette is surrounded either partially or completely by a secondspace.

A purging gas is fed inside this second space or the second chamber, ifthe cuvette is defined as a first chamber, and appropriately dischargedagain. The purging gas used must fulfil two preconditions in this case.Firstly, the purging gas must be inert or have at least essentially suchproperties, and, secondly, it is not permitted to effect any appreciableabsorption of that radiation band which is directed sensitively to themeasuring gas. The general absorption which occurs through the pluralityof the windows now occurring can be taken into account by prior gaugingor by calibration. Of course, it is also possible, going beyond this,also to take account of absorptive purging gas as well by appropriatecalibration.

The same holds for the case of leakage and for the ex-protection as suchas did for the first-named embodiment. If a leakage occurs in thecritical region leading the toxic or corrosive or combustible measuringgas, specifically in the cuvette, the leakage gas enters only the secondspace, which surrounds the measuring cuvette. Since this space or thischamber is, in addition, permanently purged by means of purging gas, asin the first example there is a steady thinning of the critical gas.Likewise, the critical gas is led out of the system, and possibly out ofthe ex-atmosphere.

As already mentioned, it holds for both variants that the second chamberis purged with inert gas or with air.

Furthermore, according to the invention it is advantageously providedboth for the first and for the second variant that a pressure higher bycomparison with the first chamber is set in the second chamber. Thisalso produces a delimitation in terms of gas dynamics by comparison withgas possibly escaping from the first chamber.

Furthermore, it is advantageously provided both for the first and forthe second variant that a flow sensor is used for monitoring the purginggas. The purging gas flow can be monitored by means of this sensor andsensitive warning sensors which, as the case may be, are connecteddownstream can detect critical gas compositions which can, in turn, havea regulating effect on the purging gas flow.

Both examples named so far relate essentially to the use of acombustible (possibly an explosive) gas in the ex-free atmosphere. Thatis to say, the ex-atmosphere exists only inside the analyzer, and iskept away from the electric systems with the aid of appropriatemeasures.

However, a second field of use is yielded by use in the so-calledex-atmosphere. In order to render such devices capable of this, as well,the devices as such are additionally protected overall in the outerregion by secondary ex-protective measures (for example pressurizingenclosure, pressuretight enclosure).

However, it is important to note in this case that the invention isessentially directed firstly to the use of toxic or corrosive orcombustible gases, which are fed to the analyzer, initiallyindependently of whether the environment is in the potentially explosiveatmosphere or the not potentially explosive atmosphere. Thesecond-mentioned case concerns the handling of toxic or corrosive orcombustible gases inside the analyzer, in which case the latter is alsoarranged, in turn, in an ex-atmosphere.

With reference to a method for operating such a gas analyzer, it isprovided according to the invention that in the case of analysis of atoxic or corrosive or combustible gas a space arranged around theanalysis or sensor unit is flowed around or through by a purging gas, anoverpressure being set in the purged space by comparison with theanalysis gas space. Consequently, for safety reasons, appropriatepressure gradients are set up which reliably prevent leakage gas fromescaping into the purging gas path and thus into the environment.

It is advantageously provided, furthermore, that purging is performedvia a regulator by virtue of the fact that fractions of toxic orcorrosive or combustible gas components in the purging gas can bedetected by a sensor and, thereupon, the throughput of purging gas canbe increased under regulation.

It is advantageously provided, furthermore, that a change in the purginggas flow or in the pressure is recorded in the test record for latercorrection, if appropriate.

It is possible thereby to achieve an influence which is to be correctedaccordingly, in particular in the case of optical gas analysis methods.It is possible to detect at least in which time phase the measurementresults are possibly unreliable.

In a further advantageous embodiment, it is specified that the entiresystem is caused to shut down in the event of the detection of anescaping gas.

In a last advantageous refinement, it is provided that underpressurepurging can also be performed. That is to say, in this case the pressureof the purging gas in the second chamber is lower than the pressure inthe first chamber, which leads the measuring gas. This results at thesame time in purging and, correspondingly, extraction.

DESCRIPTION OF THE DRAWING

FIG. 1 shows a design according to the invention with a cuvette.

FIG. 2 shows an embodiment according to the invention with a sensor.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

FIG. 1 shows the use of the invention in terms of apparatus in the caseof absorption photometry, by way of example. In this case, the systempurged by the measuring gas is the measuring cuvette 1 as such. Thelatter comprises a tubular element having a measuring gas input E and ameasuring gas output A. The entry window for the radiation from aradiation source 10 is in the region of the inlet E, and the outletwindow for the radiation passing the cuvette is in the region of themeasuring gas exit A, said radiation then being led to the detector 11.

Overall, the cuvette 1 is surrounded respectively by a second chamber 2,3, at least in the region of the entry and outlet windows. Sinceotherwise the cuvette comprises a closed metallic tube, leakages canoccur only at the built-in windows. Consequently, a purging chamber canbe provided only upstream of the entry window, and a purging chamber canbe provided upstream of the exit window. In this case the two componentchambers 2, 3 are connected at the entry window and at the exit windowto a gas line 7 such that the two component chambers 2, 3 can be flowedthrough serially by the purging gas. However, for the purpose ofenhanced protection of the system, the entire cuvette can also beprovided on the outside with a closed second chamber to which purginggas is applied, or through which purging gas is passed, as appropriate.In this case, a leakage in the cuvette region leads only to the criticalgas escaping into the purging chamber.

A purging gas monitoring unit 5 having a sensor 6 and built into thepurging system monitors whether leakage gas occurs. If this happens, thepurging or the purging throughput can be increased. This holds, inparticular, for the case of overpressure purging in which the pressurein the purging chamber region is higher than in the cuvette region.However, it is also possible to purge using underpressure, in which casethe purging gas pressure is lower than the gas pressure in the cuvette.In the second-named case, the detection of a leakage gas in the purgingsystem can lead to a further throughput, which can also lead to alowering or to a further lowering in the pressure in the purging system.

FIG. 2 shows a gas analyzer having a sensor unit and a processing unitin a housing 20. A non-explosive (for example intrinsically safe) sensoris arranged in a first sensor chamber 30 for the case in which onlycombustible gas is used. The toxic or corrosive or combustible measuringgas is introduced into this sensor chamber 30 and extracted therefrom.The sensor chamber 30 is surrounded in the way according to theinvention by a second chamber 40 which can optionally be purged. Thissecond chamber 40 is a hermetic space between the sensor chamber 30 andthe housing 20 containing the electronic system. The escape of corrosiveor toxic or combustible gas towards the analyzer is thereby prevented.The purging gas system operates in the same way as already mentioned inthe above-named example.

For the purpose of using the two analyzers in accordance with FIG.1 andFIG.2 in a potentially explosive atmosphere, the system can be furtherprotected by secondary ex-protective measures (for example pressurizingenclosure, pressuretight enclosure). It is possible overall to providean emergency shutdown unit which, upon leakage of the measuring gas,shuts down the entire system.

It is to be understood that the description of the preferredembodiment(s) is (are) intended to be only illustrative, rather thanexhaustive, of the present invention. Those of ordinary skill will beable to make certain additions, deletions, and/or modifications to theembodiment(s) of the disclosed subject matter without departing from thespirit of the invention or its scope, as defined by the appended claims.

What is claimed is:
 1. A gas analyzer comprising: (a) a gas tightchamber thru which a toxic and/or corrosive and/or combustible gas flowsand around which a second chamber is arranged, said second chamberpurged with inert gas or air and having a pressure higher or lower bycomparison with said gas tight chamber; (b) an analysis or sensor unitof a non-explosive configuration arranged in said gas tight chamber foranalyzing said toxic and/or corrosive and/or combustible gas; and (c) aprocessing unit.
 2. A method for operating a gas analyzer having ananalysis space comprising either an analysis or sensor unit or ameasuring cuvette for analyzing a toxic and/or explosive gas that mayexist in said analysis space comprising: flowing around or through aspace arranged around said analysis space of said analysis or sensorunit or said measuring cuvette, an inert gas or air as a purging gas tocreate a purged space that co-exists simultaneously around said analysisspace, while having a pressure deviating from said analysis space. 3.The method of claim 2 further comprising sealing said entire gasanalyzer off from an atmosphere disposed outside of said gas analyzer ina pressure tight fashion so that gas analyzer can be used in anexplosive environment.
 4. The method of claim 2 wherein said gasanalyzer has a measuring system and said purging gas is supplied from asystem, said method further comprising regulating said purging gas flowwhen leakage gas from said measuring system enters said purging gassystem.
 5. The method of claim 3 wherein said gas analyzer has ameasuring system and said purging gas is supplied from a system, saidmethod further comprising regulating said purging gas flow when leakagegas from said measuring system enters said purging gas system.
 6. Themethod of claim 2 further comprising picking up changes in said purginggas flow or the pressure of said purging gas and storing said changes ina test record in a fashion correlated with data measured by saidanalysis or sensor unit or said measuring cuvette at these instants. 7.The method of claim 2 further comprising shutting down as an emergencymeasure said purging gas flow in the event leakage gas is detected insaid purging gas system.
 8. A method for operating a gas analyzer havinga measuring system and an analysis space comprising either an analysisor sensor unit or a measuring cuvette, for analyzing a toxic and/orexplosive gas in said analysis space of said measuring system, saidmethod comprising: flowing around or through a space arranged aroundsaid analysis space of said analysis or sensor unit or said measuringcuvette, a purging gas flow supplied from a system to create a purgedspace that co-exists simultaneously around said analysis space, whilehaving a pressure deviating from said analysis space; and regulatingsaid purging gas flow when any leakage gas from said measuring systementers said purging gas system.
 9. A method for operating a gas analyzerhaving a measuring system and an analysis space comprising either ananalysis or sensor unit or a measuring cuvette, for analyzing a toxicand/or explosive gas in said analysis space of said measuring system,said method comprising: flowing around or through a space arrangedaround said analysis space of said analysis or sensor unit or saidmeasuring cuvette, a purging gas flow supplied from a system to create apurged space that co-exists simultaneously around said analysis space,while having a pressure deviating from said analysis space; sealing saidentire gas analyzer off from an atmosphere disposed outside of said gasanalyzer in a pressure tight fashion so that gas analyzer can be used inan explosive environment; and regulating said purging gas flow when anyleakage gas from said measuring system enters said purging gas system.10. A method for operating a gas analyzer having an analysis spacecomprising either an analysis or sensor unit or a measuring cuvette, foranalyzing a toxic and/or explosive gas in said analysis space of ameasuring system comprising: flowing around or through a space arrangedaround said analysis space of said analysis or sensor unit or saidmeasuring cuvette, a purging gas flow to create a purged space thatco-exists simultaneously around said analysis space, while having apressure deviating from said analysis space; picking up changes in saidpurging gas flow or the pressure of said purging gas; and storing saidchanges in a test record in a fashion correlated with data measured bysaid analysis or sensor unit or said measuring cuvette at theseinstants.
 11. The method of claim 8 further comprising sealing saidentire gas analyzer off from an ambient atmosphere disposed outside ofsaid gas analyzer in a pressure tight fashion so that gas analyzer canbe used in an explosive environment.
 12. The method of claim 8 furthercomprising picking up changes in said purging gas flow or the pressureof said purging gas and storing said changes in a test record in afashion correlated with data measured by said analysis or sensor unit orsaid measuring cuvette at these instants.
 13. The method of claim 8further comprising shutting down as an emergency measure said purginggas flow in the event leakage gas is detected in said purging gassystem.
 14. The method of claim 9 further comprising picking up changesin said purging gas flow or the pressure of said purging gas and storingsaid changes in a test record in a fashion correlated with data measuredby said analysis or sensor unit or said measuring cuvette at theseinstants.
 15. The method of claim 9 further comprising shutting down asan emergency measure said purging gas flow in the event leakage gas isdetected in said purging gas system.
 16. The method of claim 10 furthercomprising sealing said entire gas analyzer off from an ambientatmosphere disposed outside of said gas analyzer in a pressure tightfashion so that gas analyzer can be used in an explosive environment.17. The method of claim 10 wherein said gas analyzer has a measuringsystem and said purging gas is supplied from a system, said methodfurther comprising regulating said purging gas flow when any leakage gasfrom said measuring system enters said purging gas system.
 18. Themethod of claim 10 further comprising shutting down as an emergencymeasure said purging gas flow in the event leakage gas is detected insaid purging gas system.